This invention relates to prothesis fixturing devices, more particularly, fixturing stems for attaching a prothesis to a bone, e.g., a tibia, and a prothesis with an articulating bearing surface.
Many methods have been employed to fixture prostheses to bone, including screws, press fit, bone cement and biological fixation into porous surfaces. Currently bone cement and biological ingrowth are the preferred means of fixation. Fixturing surface geometries used include plates, fins, stems and pegs of various cross-sections. Fins form projections which in the prior art need bone preparation such as mating slots in the bone to receive the fins. This is undesirable as it entails further surgical procedures in addition to the prescribed procedures for preparing the bone for a tapered stem without such fins. Reference is made, for example, to brochures nj LCS.RTM. Tricompartmental Knee System with Porocoat.RTM., Surgical Procedure by Frederick F. Buechel, 1993, Biomedical Engineering Trust, South Orange, N.J. and Biomechanics and Design Rationale; New Jersey LCS.RTM. Knee Replacement System by Michael J. Pappas et al. 1993, Biomedical Engineering Trust which illustrate fixturing geometries and procedures for knee protheses.
The problem in these protheses is to securely attach a prothesis to bone, and yet permit the prothesis to be removed from the bone without damage thereto. More particularly, a problem is known in using cement with such protheses. For example, if the cement interlocks with depressions in the mating prothesis surface, then such interlocking may cause bone damage when the prothesis is removed. Such removal is sometimes necessitated by failure or otherwise degeneration of the prothesis-bone configuration.
Another problem encountered during the insertion procedure in attaching the prothesis via a fixturing device to the bone is alignment. Known fixturing stems are different shapes including conical, rectangular, fin among others. The mating bone cavity is similarly shaped as the corresponding stem. There is a gap between these elements when engaged to accommodate cement. These elements need to be axially aligned during the insertion process. The gap could cause misalignment of the elements during insertion or later during curing of the cement. Any misalignment could cause problems with the user of the joint, especially a knee prothesis where motion directions can be critical. Thus, it is important that the mating elements remain fixed in place and properly aligned during insertion and curing of the cement.
A still further problem is loosening of the prothesis from the bone to which the prothesis is attached during use.
The present inventor recognizes a need for improving torsional resistance between the fixturing device and the bone to which the device is attached, stability during curing of the cement or biological ingrowth, and ease of implantation and removal the device in the event of failure.
A prothesis fixturing device according to one embodiment of the present invention attaches a prothesis component including a bearing to a bone, the bone having a resected surface. The device is subject to torque loads about an axis transverse the resected surface, the torque loads tending to loosen the device relative to the bone. The device comprises a tray having a first surface for receiving the bearing and a second opposing surface and at least one wall depending from the opposing second surface for abutting the resected surface and for forming at least one recessed compartment with the second surface at a depth of at least 1.50 mm to receive a cement for bonding the tray to the bone at the resected surface, the at least one wall having a configuration for providing resistance to torque loads on the tray about the axis.
In a further embodiment a prothesis fixturing device attaches a prothesis component including a bearing to a bone, the bone having a resected surface and a cavity defining a longitudinal first axis transverse the surface, the cavity being in communication with the surface at a cavity edge, the surface and cavity for receiving the device. The device comprises a stem for receiving a prothesis and defines a second longitudinal axis. Centering means are integral with the stem forming a one piece construction for engaging the cavity edge to center the stem relative to the cavity first axis during axial insertion of the stem into the cavity.
In accordance with a further embodiment the stem has a plurality of axially extending channels having a bottom surface, the stem having a peripheral surface, the channel bottom surfaces intersecting the stem peripheral surface at a channel region distal the tray, the bottom surfaces each having a radial dimension to the second axis at least as great as the radial dimension of the intersections.
A stem according to a still further embodiment depends from a tray and defines a second longitudinal axis, the stem being dimensioned for insertion into the cavity with the axes substantially parallel, the stem having a cylindrical axially extending portion proximal the tray and a conical portion axially extending from the cylindrical portion distal the tray.